/**
 * Copyright (C) 2002-2015   The FreeCol Team
 * <p>
 * This file is part of FreeCol.
 * <p>
 * FreeCol is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 * <p>
 * FreeCol is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.common.networking;

import net.sf.freecol.common.model.Game;
import net.sf.freecol.common.model.IndianSettlement;
import net.sf.freecol.common.model.Direction;
import net.sf.freecol.common.model.Player;
import net.sf.freecol.common.model.Tile;
import net.sf.freecol.common.model.Unit;
import net.sf.freecol.common.model.Unit.MoveType;
import net.sf.freecol.server.FreeColServer;
import net.sf.freecol.server.model.ServerPlayer;

import org.w3c.dom.Element;


/**
 * The message sent when learning for the skill taught at a settlement.
 */
public class LearnSkillMessage extends DOMMessage
{

    /** The identifier of the unit that is learning. */
    private final String unitId;

    /** The direction the unit is learning in. */
    private final String directionString;


    /**
     * Create a new <code>LearnSkillMessage</code> with the
     * supplied unit and direction.
     *
     * @param unit The <code>Unit</code> that is learning.
     * @param direction The <code>Direction</code> the unit is looking.
     */
    public LearnSkillMessage( Unit unit, Direction direction )
    {
        super( getXMLElementTagName( ) );

        this.unitId = unit.getId( );
        this.directionString = String.valueOf( direction );
    }

    /**
     * Create a new <code>LearnSkillMessage</code> from a
     * supplied element.
     *
     * @param game The <code>Game</code> this message belongs to.
     * @param element The <code>Element</code> to use to create the message.
     */
    public LearnSkillMessage( Game game, Element element )
    {
        super( getXMLElementTagName( ) );

        this.unitId = element.getAttribute( "unitId" );
        this.directionString = element.getAttribute( "direction" );
    }


    /**
     * Handle a "learnSkill"-message.
     *
     * @param server The <code>FreeColServer</code> handling the message.
     * @param player The <code>Player</code> the message applies to.
     * @param connection The <code>Connection</code> message was received on.
     * @return An <code>Element</code> to update the originating
     *     player with the result of the query.
     */
    public Element handle( FreeColServer server, Player player,
                           Connection connection )
    {
        final ServerPlayer serverPlayer = server.getPlayer( connection );

        Unit unit;
        try
        {
            unit = player.getOurFreeColGameObject( unitId, Unit.class );
        }
        catch ( Exception e )
        {
            return DOMMessage.clientError( e.getMessage( ) );
        }

        Tile tile;
        try
        {
            tile = unit.getNeighbourTile( directionString );
        }
        catch ( Exception e )
        {
            return DOMMessage.clientError( e.getMessage( ) );
        }

        IndianSettlement is = tile.getIndianSettlement( );
        if ( is == null )
        {
            return DOMMessage.clientError( "There is no native settlement at: "
                                                   + tile.getId( ) );
        }

        // Do not use getMoveType (checking moves left) as the
        // preceding AskLearnSkill transaction will have already
        // zeroed the moves.
        // Consider using a transaction, so that declining restores the moves?
        MoveType type = unit.getSimpleMoveType( is.getTile( ) );
        if ( type != MoveType.ENTER_INDIAN_SETTLEMENT_WITH_FREE_COLONIST )
        {
            return DOMMessage.clientError( "Unable to enter "
                                                   + is.getName( ) + ": " + type.whyIllegal( ) );
        }

        // Learn the skill if possible.
        return server.getInGameController( )
                .learnFromIndianSettlement( serverPlayer, unit, is );
    }

    /**
     * Convert this LearnSkillMessage to XML.
     *
     * @return The XML representation of this message.
     */
    @Override
    public Element toXMLElement( )
    {
        return createMessage( getXMLElementTagName( ),
                              "unitId", unitId,
                              "direction", directionString );
    }

    /**
     * The tag name of the root element representing this object.
     *
     * @return "learnSkill".
     */
    public static String getXMLElementTagName( )
    {
        return "learnSkill";
    }
}
